Crank arm snapped in half

[bladerunner]

I check/clean my bike every month and did not notice any problems. Just as I started to go up a steep hill the other day, the left crank arm snapped in half. I am 61kg and I had a power-meter on and it recorded 480watts at the time, so nothing excessive. Has anyone ever had a similar experience?

It's a 15 years old Campagnolo Corsa Record left crank arm and it had never been crashed/damaged before. From the cross-section photo, I guess it had some kind of internal corrosion??

 

[stutue]

Not meaning to sound flippant but....

Stuff breaks

(All the time)

 

[bladerunner]

I agree totally. I've had, and I have seen, my fair share of broken parts over the years but I have never heard of a "quality" crank-arm snap in half. I just wanted to see if anyone out there can tell from the picture of the cross-section of the arm if it is due to corrosion over the years.

 

[stutue]

Don't know about corrosion...but I do know that Campag Pista cranks were quite snappy!

Good luck with whatever replaces them. Are you going HT2/UT?

 

[bladerunner]

what is ht2/ut??

 

[Bustedknuckle]

I check/clean my bike every month and did not notice any problems. Just as I started to go up a steep hill the other day, the left crank arm snapped in half. I am 61kg and I had a power-meter on and it recorded 480watts at the time, so nothing excessive. Has anyone ever had a similar experience?

It's a 15 years old Campagnolo Corsa Record left crank arm and it had never been crashed/damaged before. From the cross-section photo, I guess it had some kind of internal corrosion??

Made in mid 1980s..with the logo stamped rather than laser etched(started about 1987/8) so it's almost 30 years old....

 

[avanti]

I was officiating at a So. California bike race and I saw a Campagnolo arm with a break about an inch above the pedal (in the early 1980s)

 

[stutue]

what is ht2/ut??

Hollowtech2/ Ultratorque...

Shimano and Campagnolos external bearing systems.

 

[bladerunner]

I have Dura Ace external bearings cranks on my race bike and I like it but I always felt that the Campag Corsa Record cranks were more solid (until it snapped!!).

I bought the Corsa Record cranks new 15 years ago and I've been using them on my training bike ever since. I have seen other cranks crack/break near the pedal area but I just never thought a solid aluminium arm can get eroded so badly for it to snap in half.

 

[Master50]

the black parts were the first to fail and they started to fail a while ago. might have been a defect? The shiny bit were the fast failure. the failure mode can probably explained just from the pictures. Dark areas are oxidization so there was a void or a crack to allow oxygen into that area. Weakened the rest was forced to carry greater load and eventually failed catastrophically.
Since you did not see a crack it might have been a defect and that is only based on the long time that oxidization would take. What are they?15 to 20 years old?
Seen super record cranks do that. Actually have seen that on most aluminum cranks at some point.

aluminum breaks from fatigue. you just pushed that arm to failure sooner than it was likely intended to.
Good reason to remember many bars are aluminum.

 

[winkybiker]

I broke a Campy Gran Sport crank in exactly the same manner many years ago. (Crashed hard when it happened, too. I was cranking slowly on a steep gradient, but still...Ouch) I guess the crank was about 7 or 8 years old at the time. The break looked exactly like yours. It had obviously been cracked for a while and you could see the darker oxidised (and dirty?) colour of the older fracture quite clearly against the fresh final failure. I think the cracking starts small and progresses gradually over many months, probably exacerbated by corrosion.

As per Master50 - all aluminium components that are under stress will eventually fail. It is just a matter of when.

 

[Captain Serious]

Hmm, there's a fair chance there was a visible crack on the crank before it busted, even a teeeeny one.

I only busted one crank, which was a very old Mavic. At the time -- about 15 years ago -- I didn't even know that cranks could break, so I never checked for imperfections.

I've just found this crack on a few sets of my Dura-Ace 7800 cranks, but this is the worst one.

 

[DirtyWorks]

I have Dura Ace external bearings cranks on my race bike and I like it but I always felt that the Campag Corsa Record cranks were more solid (until it snapped!!).

I bought the Corsa Record cranks new 15 years ago and I've been using them on my training bike ever since. I have seen other cranks crack/break near the pedal area but I just never thought a solid aluminium arm can get eroded so badly for it to snap in half.

It's a cast/forged alloy product and seems like it was not cast correctly. It is entirely possible there was no external clue before the failure. Cast aluminum has peculiar failure properties depending on the alloy.

Hopefully you were physically okay.

 

[Hugh Januss]

I check/clean my bike every month and did not notice any problems. Just as I started to go up a steep hill the other day, the left crank arm snapped in half. I am 61kg and I had a power-meter on and it recorded 480watts at the time, so nothing excessive. Has anyone ever had a similar experience?

It's a 15 years old Campagnolo Corsa Record left crank arm and it had never been crashed/damaged before. From the cross-section photo, I guess it had some kind of internal corrosion??

I broke Nuovo Record arms the same way on 2 separate occasions in the 70s but none since. More pedal axles. The black area on the picture that I left up suggests to me that it was cracked for awhile more than likely from tagging a pedal in a corner at some point.

 

[hiero2]

Hmm, there's a fair chance there was a visible crack on the crank before it busted, even a teeeeny one.

I only busted one crank, which was a very old Mavic. At the time -- about 15 years ago -- I didn't even know that cranks could break, so I never checked for imperfections.

I've just found this crack on a few sets of my Dura-Ace 7800 cranks, but this is the worst one.

Personally, I think I would discard those cracked 7800 cranks. After all, aluminum doesn't give you any warning when it goes. Just boom.

I've never seen a crank arm snap. I've heard stories others tell, never seen it. It does bring to mind aircraft inspection when I was working for a commercial airline. There would be cracks in wing spars etc - older aircraft usually. They still flew - since the alloys were not of the catastrophic failure variety (like these aluminum alloys).

I have discarded alu alloy rims with stress cracks, as that means to me that they are about to fail - age or stress or both.

 

[ustabe]

This is where old Campagnolo Record cranks fail.

Sure enough, the Super Record crank on my old Masi has 'em.

 

[avanti]

This is where old Campagnolo Record cranks fail.

Sure enough, the Super Record crank on my old Masi has 'em.

I just checked my Campagnol Pista cranks and they have a similar looking sharp edge (but no visible cracks). Sharp edges are where cracks usually start and I'm surprised that Campagnolo allows them. I'm going to take a smooth file and add a radius or chamfer in this area.